In accordance with the improvement in the performance and the increase in the power of an automobile in recent years, there has been noted the application of the so-called "traction control system (TCS)", in which a predetermined actuator, such as an electric motor, is used for opening or closing a throttle valve, so that the opening degree of the throttle valve may be controlled by first introducing the opening degree of an accelerator pedal as data into a control unit, such as a micro-computer, to subject it to a predetermined arithmetic operation to calculate a desired opening degree of the throttle valve and then by feeding the calculated opening degree of the throttle valve to the actuator.
This system requires an actuator for controlling the opening degree of the throttle valve, as described hereinbefore. The actuator of this kind known per se is exemplified by using a D.C. motor, as disclosed in Japanese laying-Open Patent Publication No. Sho 61-93251.
The actuator using the D.C. motor is considered advantageous from the point of view of response, cost and size so that it has a tendency to be widely adopted.
The above prior art, however, has taken no consideration into the influences of the operation condition changes at the driven mechanism, such as the throttle valve of the actuator, thus raising a problem in the high precision of the throttle opening control.